Exploring, drilling and completing hydrocarbon and other wells are generally complicated, time consuming and ultimately very expensive endeavors. In recognition of these expenses, added emphasis has been placed on efficiencies associated with well completions and maintenance over the life of the well. Over the years, ever increasing well depths and sophisticated architecture have made reductions in time and effort spent in completions and maintenance operations of even greater focus.
Perforating and fracturing applications in a cased well, generally during well completion, constitute one such area where significant amounts of time and effort are spent, particularly as increases in well depths and sophisticated architecture are encountered. These applications involve the positioning of a bridge plug downhole of a well section to be perforated and fractured. Positioning of the bridge plug may be aided by pumping a driving fluid through the well. This may be particularly helpful where the plug is being advanced through a horizontal section of the well.
Once in place, equipment at the oilfield surface may communicate with the plug assembly over conventional wireline so as to direct setting of the plug. Such setting may include expanding slips and a seal of the assembly for anchoring and sealing of the plug respectively. Once anchored and sealed, a perforation application may take place above the bridge plug so as to provide perforations through the casing in the well section. Similarly, a fracturing application directing fracture fluid through the casing perforations and into the adjacent formation may follow. This process may be repeated, generally starting from the terminal end of the well and moving uphole section by section, until the casing and formation have been configured and treated as desired.
The presence of the set bridge plug in below the well section as indicated above keeps the high pressure perforating and fracturing applications from affecting well sections below the plug. Indeed, even though the noted applications are likely to generate well over 5,000 psi, the well section below the plug is kept isolated from the section thereabove. This degree of isolation is achieved largely due to the use of durable metal features of the plug, including the above noted slips, as well as a central mandrel.
Unfortunately, unlike setting of the bridge plug, wireline communication is unavailable for releasing the plug. Rather, due to the high pressure nature of the applications and the degree of anchoring required of the plug, it is generally configured for near permanent placement once set. As a result, removal of a bridge plug requires follow on drilling out of the plug. Once more, where the plug is set in a horizontal section of the well, removal of the plug may be particularly challenging. Unlike the initial positioning of the bridge plug, which may be aided by pumping fluid through the well, no significant tool or technique is readily available to aid in drillably removing the plug. Indeed, due to the physical orientation of the plug relative the oilfield surface equipment, each drill-out of a plug in a horizontal well section may require hours of dedicated manpower and drilling equipment.
Depending on the particular architecture of the well, several horizontal bridge plug drill-outs, as well as dozens of vertical drill-outs may take place over the course of conventional perforating and fracturing operations for a given cased well. All in all, this may add up to several days and several hundred thousand dollars in added manpower and equipment expenses, solely dedicated to bridge plug drill-out. Furthermore, even with such expenses incurred, the most terminal or downhole horizontal plugs are often left in place, with the drill-out application unable to achieve complete plug removal, thus cutting off access to the last several hundred feet of the well.
Efforts have been made to reduce expenses associated with time, manpower, and equipment that are dedicated to bridge plug drill-outs as described above. For example, many bridge plugs today include parts made up of fiberglass based materials which readily degrade during drill-out. However, use of such materials for the above noted slips and/or mandrel may risk plug failure during high pressure perforating or fracturing. Such failure would likely require an additional clean out application and subsequent positioning and setting of an entirely new bridge plug, all at considerable time and expense. Thus, in order to avoid such risks, conventional bridge plugs generally continue to require time consuming and labor intensive drill-out for removal, particularly in the case of horizontally positioned plugs.